1. Field of the Invention
The present invention relates to an adhesive composition which is particularly suited for using at a step of die-bonding a semiconductor element (semiconductor chip) on an organic substrate or a lead frame and a step of dicing a silicon wafer and the like and die-bonding a semiconductor chip on an organic substrate or a lead frame, an adhesive sheet having an adhesive layer comprising the above adhesive composition and a production process for a semiconductor device using the above adhesive sheet.
2. Description of the Related Art
A semiconductor wafer of silicon, gallium arsenide or the like is produced in a large size, and this wafer is cut and separated (dicing) into small element pieces (IC chips) of devices and then transferred to a bonding step which is a subsequent step. In this case, the semiconductor wafer is subjected to the respective steps of dicing, washing, drying, expanding and picking-up in the state that it is adhered and fixed in advance on an adhesive sheet, and then it is transferred to a bonding step which is a subsequent step. Furthermore, for such purposes as protecting a semiconductor chip from the surrounding environment and making it into a shape easily mountable on a printed board, a semiconductor package is produced, in some cases, by sealing a substrate on which an IC chip is bonded with a mold resin after the bonding step.
In order to simplify the picking-up step and the bonding step among the above steps, various adhesive sheets for dicing and die-bonding which are provided with both a wafer-fixing function and a die(IC chip)-adhering function at the same time are proposed (for example, refer to patent documents 1 to 4).
Adhesive sheets comprising an adhesive layer comprising a specific composition and a base material are disclosed in the patent documents 1 to 4. The above adhesive layer has a function of fixing a wafer in dicing the wafer, and irradiation thereof with an energy beam reduces an adhesive strength thereof and makes it possible to control the adhesive strength between the adhesive layer and the base material, so that when picking up the chip after finishing dicing, the adhesive layer is peeled off together with the chip. When the IC chip provided with the adhesive layer is mounted on a substrate and heated, an adhesive strength of a thermosetting resin contained in the adhesive layer is revealed to complete adhesion between the IC chip and the substrate.
The adhesive sheets disclosed in the patent documents described above enables so-called direct die-bonding and makes it possible to omit a step of coating an adhesive for adhering a die.
In recent years, a requirement for the reduction in thickness of semiconductor devices has become quite intense. Further, not only an IC chip but also an adhesive layer itself is required to be reduced in thickness. This is because the thickness of the adhesive layer that interposes between an IC chip and a substrate can not be neglected in a structure of a semiconductor device in which a number of IC chips are stacked.
Further, conventional adhesive sheets have poor storage stability because a curing component contained in the adhesive layer instantly reacts during the storage even at room temperature. Therefore, an adhesive sheet has been required that can be kept in storage at room temperature for an extended period of time from a few weeks to about one month.
To meet the requirement, there has been developed an adhesive sheet employing a granular dispersive latent thermosetting agent or thermosetting accelerating agent that has good storage stability.
However, the granular dispersive latent thermosetting agent or thermosetting accelerating agent is difficult to be dispersed uniformly in an adhesive layer. It is difficult to obtain smooth coating surface in the case of an adhesive layer of which the thickness is thin to the extent that the particle size can be no longer neglected. In addition, the structures of resultant thermoset articles are likely to be non-uniform and the properties thereof are largely fluctuated, which are of problem.
In the technique disclosed in the Patent Documents above, an adhesive composition having storage stability is attained by using a granular latent thermosetting agent. However, when the granular latent thermosetting agent is used, it is physically difficult to prepare an adhesive sheet with an adhesive layer having a thickness of less than or equal to the particle size of the thermosetting agent, and thus the recent requirement for reduction in thickness of semiconductor devices is not satisfied.
In a surface mounting carried out in connection of electronic parts in recent years, a surface mounting method in which the whole part of a package is exposed to high temperature of not lower than a melting point of a solder is carried out(reflow process). In recent years, a mounting temperature is elevated from 240° C. which has so far been carried out to 260° C. due to transfer to a solder containing no lead from the viewpoint of attentions to the environment to increase a stress produced in the inside of a semiconductor package, and the risk of causing package crack is further elevated.
Namely, with the reduction in thickness of semiconductor chips and the elevation of mounting temperature, an adhesive sheet having a thin adhesive layer and allowing the production of semiconductor devices endurable to a severe hot and humid environment is required. However, as described above, it is difficult to provide an adhesive sheet having a thin adhesive layer with the conventional adhesive compositions using the granular thermosetting agent.    Patent document 1: JP-A-1990-32181    Patent document 2: JP-A-1996-239636    Patent document 3: JP-A-1998-8001    Patent document 4: JP-A-2000-17246